[Tutor] How to test for the existence of a table in a sqlite3 db?

[boB Stepp]

I want to use Alan's (and others') idea to run a SQL file to create a
table if that table does not exist.  Alan suggested using
executescript() to do this.  I misunderstood Alan and thought that
this would take a filename and execute it.  Instead, it appears that I
must pass to it a string which is a SQL script.  So after lots of
fooling around in the interpreter I arrived at:

py3: import sqlite3
py3: conn = sqlite3.connect(':memory:')
py3: c = conn.cursor()
py3: try:
... c.execute('select * from BloodPressureReadings')
... except sqlite3.OperationalError:
... with open('create_sqlite3_db.sql') as f:
... sql = f.read()
... c.executescript(sql)
...


The file 'create_sqlite3_db.sql' contains:

CREATE TABLE BloodPressureReadings (
ReadingID INTEGER PRIMARY KEY,
Date TEXT,
Time TEXT,
SystolicBP INTEGER,
DiastolicBP INTEGER,
Comments TEXT);

So at this point I am only creating an empty table.

The above "works", but my "try" check is awful!  What can I replace it
with to just see if there is *any* table in the chosen database?  In
the code Peter supplied in the thread, "How is database creation
normally handled?", he used in his function, "ensure_db(filename)":

cursor.execute("create table if not exists addresses (name, email);")

which is sweet, but I don't see how I can apply this idea if I insist
on using a SQL file to create my table(s).

BTW, in the docs at https://docs.python.org/3/library/sqlite3.html I
found no mention of the actual exception I caught, "OperationalError".
Should not this be in the docs?

-- 
boB
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Re: [Tutor] problem with program

[Alan Gauld via Tutor]

On 13/10/17 18:53, Alan Gauld via Tutor wrote:
> On 13/10/17 13:04, Chris Coleman wrote:
> 
>> def_init_(self,chat):
> 
>> File "scripts/bird.py", line 4
>> def_init_(self,chat):
>>   ^
>> SyntaxError: invalid syntax
> 
> There are two problems here.

I meant to add that the syntax error is the colon
at the end. Python sees what you've written as a
function call but it doesn't know what to do
with the colon.

But if you add the space it sees it as a method
definition and all is well.

And once you add the second underscores it then
recognises it as a dunder method definition and
all is even better. :-)

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] using while loop for read process memory

[Michael C]

Sorry Alan, Steve, everyone

Can you take a look of this please?



Here is my question about the memory:

So I have a base address of a chunk of memory from it's size, from
VirtualQueryEx
(if you dont use windows, it's ok, it's not about how u get these values,
because I think
the base concept is the same)

start = mbi.BaseAddress
finish = mbi.RegionSize

So at this time, I use while and this is how it looks like

while index < finish:
   # access the memory here:
   while memory function( index)
   # then index += 1, for the inner loop

## this line complete the outer while loop
index += mbi.RegionSize


so Why did I put down index += 1  ?

That's because what I think about the memory looks like this
(short)(int)(double)(int)(int)(int)(double)  and so on,

since I can't predict which address is the beginning of a double, the only
way
to deal with that is to use increment by 1.

Now, from what I have been reading, it seems there is a better way to do it,
for instance, a for loop.

for(start,finish, 8)

why 8? because double begins at exact 0 or multiple of 8 bytes, right?

On Thu, Oct 12, 2017 at 6:54 PM, Michael C 
wrote:

> Here is my question about the memory:
>
> So I have a base address of a chunk of memory from it's size, from
> VirtualQueryEx
> (if you dont use windows, it's ok, it's not about how u get these values,
> because I think
> the base concept is the same)
>
> start = mbi.BaseAddress
> finish = mbi.RegionSize
>
> So at this time, I use while and this is how it looks like
>
> while index < finish:
># access the memory here:
>while memory function( index)
># then index += 1, for the inner loop
>
> ## this line complete the outer while loop
> index += mbi.RegionSize
>
>
> so Why did I put down index += 1  ?
>
> That's because what I think about the memory looks like this
> (short)(int)(double)(int)(int)(int)(double)  and so on,
>
> since I can't predict which address is the beginning of a double, the only
> way
> to deal with that is to use increment by 1.
>
> Now, from what I have been reading, it seems there is a better way to do
> it,
> for instance, a for loop.
>
> for(start,finish, 8)
>
> why 8? because double begins at exact 0 or multiple of 8 bytes, right?
>
>
>
> On Sun, Oct 8, 2017 at 4:46 PM, Alan Gauld via Tutor 
> wrote:
>
>> On 08/10/17 20:18, Michael C wrote:
>> > This is the red part
>> >   index = current_address
>> > end = current_address + mbi.RegionSize
>> >
>> > while index < end:
>> > if ReadProcessMemory(Process, index, ctypes.byref(buffer), \
>> >  ctypes.sizeof(buffer),
>> > ctypes.byref(nread)):
>> > ## value comparison to be implemented.
>> > pass
>> > else:
>> > raise ctypes.WinError(ctypes.get_last_error())
>> >
>> > index += 1
>>
>> I haven't been following this closely so may be way off here,
>> but does this mean you are incrementing the memory address
>> by 1? If so you are only increasing the pointer by 1 byte
>> but you are, presumably, reading multiple bytes at a time
>> (the size of the buffer presumably).
>>
>> Do you perhaps need to treat the buffer as a byte array
>> and use something like the struct module to decode it?
>> (assuming you know what you are reading...?)
>>
>> But I may be way off, I'm just going on a cursory look.
>>
>> --
>> Alan G
>> Author of the Learn to Program web site
>> http://www.alan-g.me.uk/
>> http://www.amazon.com/author/alan_gauld
>> Follow my photo-blog on Flickr at:
>> http://www.flickr.com/photos/alangauldphotos
>>
>>
>> ___
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>> To unsubscribe or change subscription options:
>> https://mail.python.org/mailman/listinfo/tutor
>>
>
>
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Re: [Tutor] problem with program

[Mark Lawrence via Tutor]

On 13/10/17 13:04, Chris Coleman wrote:

just learning python as my first programming language.  going through the
book "python in easy steps" by mike mcgrath.  i am going through the
programs in chapter 7 and can't get them to work.  here is the first one in
the chapter:
class Bird:
 '''A base class to define bird properties.'''
 count=0
 def_init_(self,chat):
 self.sound=chat
 Bird.count+=1
 def talk(self):
 return self.sound
from Bird import*
print('\nClass Instances Of:\n',Bird._doc_)
polly=Bird('Squawk,squawk!')
print('\nNumber Of Birds:',polly.count)
print('Polly Says:',polly.talk())
harry=Bird('Tweet,tweet!')
print('\nNumber Of Birds:',harry.count)
print('Harry Says:',harry.talk())

i am getting this error message:

File "scripts/bird.py", line 4
 def_init_(self,chat):


You need a space between the `def` and the `__init__`.


   ^
SyntaxError: invalid syntax

what am i doing or not doing that is causing this?




--
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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[Tutor] OT: New book on pytest

[boB Stepp]

I just got the book in The Pragmatic Programmers series, "Python
Testing with pytest -- Simple, Rapid, Effective, and Scalable" by
Brian Okken, c. 2017.  I've gone through about three chapters so far
and I am really liking this book and pytest.  Now that I am playing
around with pytest, I must say I like its simpler ways of doing
things.  And I haven't lost anything!  It runs all of my existing
unittest code just fine.  Thought I would mention this book in case
anyone on the Tutor list has thought about trying pytest, but wanted a
book on it.

-- 
boB
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Re: [Tutor] problem with program

[Alan Gauld via Tutor]

On 13/10/17 13:04, Chris Coleman wrote:

> def_init_(self,chat):

> File "scripts/bird.py", line 4
> def_init_(self,chat):
>   ^
> SyntaxError: invalid syntax

There are two problems here.

The first is that you need a space after the def.
The second is that there should be two underscores
on each side of init, so:

def __init__():

The double underscore is a common structure in
Python that indicates a method that is handled
in a special way by Python, they are often
called "dunder" methods. But it often catches
beginners out, especially if your tutorial font
does not make the double underscore obvious.

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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[Tutor] problem with program

[Chris Coleman]

just learning python as my first programming language.  going through the
book "python in easy steps" by mike mcgrath.  i am going through the
programs in chapter 7 and can't get them to work.  here is the first one in
the chapter:
class Bird:
'''A base class to define bird properties.'''
count=0
def_init_(self,chat):
self.sound=chat
Bird.count+=1
def talk(self):
return self.sound
from Bird import*
print('\nClass Instances Of:\n',Bird._doc_)
polly=Bird('Squawk,squawk!')
print('\nNumber Of Birds:',polly.count)
print('Polly Says:',polly.talk())
harry=Bird('Tweet,tweet!')
print('\nNumber Of Birds:',harry.count)
print('Harry Says:',harry.talk())

i am getting this error message:

File "scripts/bird.py", line 4
def_init_(self,chat):
  ^
SyntaxError: invalid syntax

what am i doing or not doing that is causing this?
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Re: [Tutor] sibling import

[Alex Kleider]

On 2017-10-12 15:58, Mats Wichmann wrote:

On 10/12/2017 05:15 AM, Atar new wrote:

Hi Team,

Here is my problem. I want to use sibling import but it is not working 
. I

know taht if we add the directory in sys.path ,it will work.

But I have to package the whole application and will create a setup.py 
file

out of it .
What is the standard way to do it?


   1. mkdir A
   2. mkdir B
   3.
   4. touch A/__init__.py
   5. touch B/__init__.py
   6.
   7. touch A/foo.py
   8. touch B/bar.py
   9.
   10. cat B/bar.py
   11. from A import foo
   12.
   13.
   14. python B/bar.py
   15. ImportError: No module named A



Thanks
Anju


This isn't the way: from the context of bar.py in B, there is no A.  
You

generally speaking want a relative import (from .A import foo) for
modern python versions, but because of the path structure you've set 
up,
even that won't work, the script doing the importing would need to be 
in

the top directory of your package. "Sibling" imports just don't work
well.  There was a PEP somewhere about this, which as I recall required
some horrid looking hack.

So with a bit of hunting,
https://www.python.org/dev/peps/pep-0366
and more reading at
https://www.python.org/dev/peps/pep-0338


I think Anju can solve his problem simply by adding his working 
directory (parent of A and B) to PYTHONPATH.
Some one on this list some time ago provided me with the following bash 
magic to accomplish this:


export PYTHONPATH="${PYTHONPATH:+$PYTHONPATH:}$(pwd)"
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Re: [Tutor] coding help with maxwell-boltzmann distribution

[D . V . N . Sarma డి . వి . ఎన్ . శర్మ]

Yes we can vectorize.

regards,
Sarma.

On Fri, Oct 13, 2017 at 9:43 PM, Peter Otten <__pete...@web.de> wrote:

> D.V.N.Sarma డి.వి.ఎన్.శర్మ wrote:
> > f = np.zeros(40)
> > v = np.arange(0,4,0.1)
> > for i in np.arange(0, 40):
> > f[i] = v[i]**2*(np.exp(-v[i]**2))
>
> Note that you can write this without Python loop as
>
> v = np.arange(0, 4, 0.1)
> f = v**2 * np.exp(-v**2)
>
>
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Re: [Tutor] coding help with maxwell-boltzmann distribution

[Peter Otten]

D.V.N.Sarma డి.వి.ఎన్.శర్మ wrote:
> f = np.zeros(40)
> v = np.arange(0,4,0.1)
> for i in np.arange(0, 40):
> f[i] = v[i]**2*(np.exp(-v[i]**2))

Note that you can write this without Python loop as

v = np.arange(0, 4, 0.1)
f = v**2 * np.exp(-v**2)


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Re: [Tutor] coding help with maxwell-boltzmann distribution

[D . V . N . Sarma డి . వి . ఎన్ . శర్మ]

Except for some constants the essential behaviour of Maxweell-Boltzmann
distribution is determined by
v**2 * exp(-v**2)
The following code will gove you
a plot of the shape of the curve.

from matplotlib import pyplot as plt
import numpy as np
f = np.zeros(40)
v = np.arange(0,4,0.1)
for i in np.arange(0, 40):
f[i] = v[i]**2*(np.exp(-v[i]**2))
plt.plot(v,f)
plt.show()

regards,
Sarma.

On Fri, Oct 13, 2017 at 11:28 AM, Mark Lawrence via Tutor 
wrote:

> On 12/10/17 21:22, Cameron McKay wrote:
>
>> Hello,
>>
>> I've never used python trying to plot a graph. Thus I am having
>> difficulties trying to plot the maxwell-boltzmann distribution. right now
>> i've defined the y-axis given the probability, but the difficult part is
>> trying to plot x in the form of:
>>
>> x = v/(2kT/m)^(1/2)
>>
>> before i used the linspace function but i believe that was wrong as it
>> just
>> gave me an exponential growth function as i need a bellcurve.
>>
>> Thanks for looking into this,
>>
>> Cameron
>>
>>
> Hopefully this helps https://docs.scipy.org/doc/sci
> py/reference/generated/scipy.stats.maxwell.html
>
> --
> My fellow Pythonistas, ask not what our language can do for you, ask
> what you can do for our language.
>
> Mark Lawrence
>
>
> ___
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Re: [Tutor] using while loop for read process memory

[Alan Gauld via Tutor]

On 13/10/17 02:58, Michael C wrote:

>         end = current_address + mbi.RegionSize - 7
> 
> then it doesn't complain anymore. I think it's because I ran this in a
> while loop with start += 1
> so in the last 7 bytes, I'd be reading past the end of this memory chunk.
> 
> Is this right?

Yes, almost certainly. That's what both Steve and I were
alluding to in our earlier responses, you were incrementing
by 1 byte but reading more than one byte so there was a
high probability of you reading past the end.

But subtracting 7 is only the correct answer if you
are always reading 8 byte blocks, if you are reading
different length blocks (for int/short/char etc) then
you might need to do some kind of dynamic check based
on sizeof(chunk)...

if index+sizeof(chunk) > end
   data = read(chunk)
else break

-- 
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
http://www.flickr.com/photos/alangauldphotos


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Re: [Tutor] using while loop for read process memory

[Michael C]

in fact, when I am using this:

end = start + mbi.RegionSize

I was getting error from the ReadProcessMemory function, and I couldn't
figure it out why.
Until I did this:
end = current_address + mbi.RegionSize - 7

then it doesn't complain anymore. I think it's because I ran this in a
while loop with start += 1
so in the last 7 bytes, I'd be reading past the end of this memory chunk.

Is this right?

On Thu, Oct 12, 2017 at 6:54 PM, Michael C 
wrote:

> Here is my question about the memory:
>
> So I have a base address of a chunk of memory from it's size, from
> VirtualQueryEx
> (if you dont use windows, it's ok, it's not about how u get these values,
> because I think
> the base concept is the same)
>
> start = mbi.BaseAddress
> finish = mbi.RegionSize
>
> So at this time, I use while and this is how it looks like
>
> while index < finish:
># access the memory here:
>while memory function( index)
># then index += 1, for the inner loop
>
> ## this line complete the outer while loop
> index += mbi.RegionSize
>
>
> so Why did I put down index += 1  ?
>
> That's because what I think about the memory looks like this
> (short)(int)(double)(int)(int)(int)(double)  and so on,
>
> since I can't predict which address is the beginning of a double, the only
> way
> to deal with that is to use increment by 1.
>
> Now, from what I have been reading, it seems there is a better way to do
> it,
> for instance, a for loop.
>
> for(start,finish, 8)
>
> why 8? because double begins at exact 0 or multiple of 8 bytes, right?
>
>
>
> On Sun, Oct 8, 2017 at 4:46 PM, Alan Gauld via Tutor 
> wrote:
>
>> On 08/10/17 20:18, Michael C wrote:
>> > This is the red part
>> >   index = current_address
>> > end = current_address + mbi.RegionSize
>> >
>> > while index < end:
>> > if ReadProcessMemory(Process, index, ctypes.byref(buffer), \
>> >  ctypes.sizeof(buffer),
>> > ctypes.byref(nread)):
>> > ## value comparison to be implemented.
>> > pass
>> > else:
>> > raise ctypes.WinError(ctypes.get_last_error())
>> >
>> > index += 1
>>
>> I haven't been following this closely so may be way off here,
>> but does this mean you are incrementing the memory address
>> by 1? If so you are only increasing the pointer by 1 byte
>> but you are, presumably, reading multiple bytes at a time
>> (the size of the buffer presumably).
>>
>> Do you perhaps need to treat the buffer as a byte array
>> and use something like the struct module to decode it?
>> (assuming you know what you are reading...?)
>>
>> But I may be way off, I'm just going on a cursory look.
>>
>> --
>> Alan G
>> Author of the Learn to Program web site
>> http://www.alan-g.me.uk/
>> http://www.amazon.com/author/alan_gauld
>> Follow my photo-blog on Flickr at:
>> http://www.flickr.com/photos/alangauldphotos
>>
>>
>> ___
>> Tutor maillist  -  Tutor@python.org
>> To unsubscribe or change subscription options:
>> https://mail.python.org/mailman/listinfo/tutor
>>
>
>
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Re: [Tutor] using while loop for read process memory

[Michael C]

Here is my question about the memory:

So I have a base address of a chunk of memory from it's size, from
VirtualQueryEx
(if you dont use windows, it's ok, it's not about how u get these values,
because I think
the base concept is the same)

start = mbi.BaseAddress
finish = mbi.RegionSize

So at this time, I use while and this is how it looks like

while index < finish:
   # access the memory here:
   while memory function( index)
   # then index += 1, for the inner loop

## this line complete the outer while loop
index += mbi.RegionSize


so Why did I put down index += 1  ?

That's because what I think about the memory looks like this
(short)(int)(double)(int)(int)(int)(double)  and so on,

since I can't predict which address is the beginning of a double, the only
way
to deal with that is to use increment by 1.

Now, from what I have been reading, it seems there is a better way to do it,
for instance, a for loop.

for(start,finish, 8)

why 8? because double begins at exact 0 or multiple of 8 bytes, right?



On Sun, Oct 8, 2017 at 4:46 PM, Alan Gauld via Tutor 
wrote:

> On 08/10/17 20:18, Michael C wrote:
> > This is the red part
> >   index = current_address
> > end = current_address + mbi.RegionSize
> >
> > while index < end:
> > if ReadProcessMemory(Process, index, ctypes.byref(buffer), \
> >  ctypes.sizeof(buffer),
> > ctypes.byref(nread)):
> > ## value comparison to be implemented.
> > pass
> > else:
> > raise ctypes.WinError(ctypes.get_last_error())
> >
> > index += 1
>
> I haven't been following this closely so may be way off here,
> but does this mean you are incrementing the memory address
> by 1? If so you are only increasing the pointer by 1 byte
> but you are, presumably, reading multiple bytes at a time
> (the size of the buffer presumably).
>
> Do you perhaps need to treat the buffer as a byte array
> and use something like the struct module to decode it?
> (assuming you know what you are reading...?)
>
> But I may be way off, I'm just going on a cursory look.
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
> ___
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Re: [Tutor] coding help with maxwell-boltzmann distribution

[Mark Lawrence via Tutor]

On 12/10/17 21:22, Cameron McKay wrote:

Hello,

I've never used python trying to plot a graph. Thus I am having
difficulties trying to plot the maxwell-boltzmann distribution. right now
i've defined the y-axis given the probability, but the difficult part is
trying to plot x in the form of:

x = v/(2kT/m)^(1/2)

before i used the linspace function but i believe that was wrong as it just
gave me an exponential growth function as i need a bellcurve.

Thanks for looking into this,

Cameron



Hopefully this helps 
https://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.maxwell.html


--
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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